The present invention relates to user interface control and haptics generation.
Haptics refers to the sense of touch. In electronic devices, haptics relates to providing a touch sensory feedback to the user. Electronic devices incorporating haptics may include cell phones, PDAs, gaming devices, etc. The user interacts with electronic devices through a user interface, such as a touch screen; however, the user often does not know if the user's desired function was recognized or is being performed by the electronic device. Thus, electronic devices generate a haptic feedback in the form of a vibro-tactile sensation (e.g. a simulated “click”) to alert the user of the electronic device's performance. Stated differently, haptic feedback lets the user know what is going on with the electronic device. In a gaming electronic device, for example, haptics can provide a sensory stimuli according to game interactions.
Haptic feedback can be generated by electro-mechanical systems. An electrical system produces a drive signal that will then cause a mechanical system to produce the haptic effect. For example, an actuator incorporating a moving mass can be used to generate haptic effects. A linear resonant actuator (LRA) is an example of one such actuator in which a moving mass is spring loaded. For efficient haptic generation using an LRA, the spring loaded mass may be driven at its mechanical resonant frequency, which is the natural vibration frequency of the spring loaded mass. Also, the magnitude of the haptic effect may be controlled by the amplitude of the actuator driving signal.
In some conventional systems, BEMF (Back Electromotive Force) is used to tune the actuator. BEMF is an electrical signal that is induced into a the electrical connections of the motor by the movement of a permanent magnet (which as a mass) relative to a stationary wire wound coil. In theory, the BEMF signal will have electrical properties (e.g., frequency, amplitude) that correspond to the mechanical vibrations in the actuator. However, the BEMF measurements may be unreliable at times because of electrical interferences in the system and, thus, may not provide accurate representation of the vibrations.
Hence, the inventors recognized a need in the art for an adaptive haptic effect generation technique based on accurate representations of the mechanical vibrations.